Stable Disease in Cancer Treatment

Cancer doctors use the term stable disease to describe a tumor that is neither growing nor shrinking. Specifically, it means that there was neither an increase in size of more than 20% nor a decrease in size of more than 30% since the initial baseline measurement. Stable disease also means that no new tumors have developed and that cancer has not metastasized (spread) to other parts of the body.

Stable disease falls in the spectrum of treatment responses. And though people may be discouraged to hear that a tumor has not shrunk considerably, stable disease can sometimes be a good sign. For example, if a tumor was expected to grow and did not, stable disease may indicate that a therapy is, indeed, working.

While stable disease can have significant meaning, there are some limitations when it comes to defining it. Newer treatments (such as targeted therapies and immunotherapy) are also altering the ways doctors consider the idea of stable disease.

Defining Stable Disease

To better understand stable disease, it is important to know where on the spectrum the term falls.

Stable disease does not necessarily mean that the tumor is unchanged. It only means that the changes are not enough to suggest there is either disease progression or a partial response to treatment.

Most health authorities require that there be a period of at least four weeks between tumor evaluations before stable disease can be confidently established.

Limitations

As confusing as it may seem, a tumor can be considered stable even if it has, for example, increased in size by 10% to 20%.

The reason for this is that the tools used to measure the size of a tumor do so indirectly. Rather than looking at a tumor directly via surgery or laparoscopy, doctors will monitor the size with imaging tests such as computed tomography (CT) and positron emission tomography (PET) scans.

In the end, the size of a tumor can sometimes be diagnosed differently by two different radiologists reading the same films. The tumor may also be imaged from slightly different angles between scans, altering the perception of size.

Measuring the Response

Stable disease doesn't necessarily mean that a treatment isn't working. What it means can vary significantly depending on the type of tumor you have, the particular treatment you are receiving, and your response to other treatments in the past.

Stable disease may mean that a treatment isn't working, but it may also mean that a treatment is working very well.

If a tumor was expected to have grown in the interval between two scans and has remained stable, it may mean that the treatment is effective, even if there is not much of a change seen on imaging. Cancer may also be stable if the tumor was at risk of metastasis following a prior scan but no such spread was observed.

Impact of Targeted Therapies

Up until the last decade or so, clinical trials often required evidence of a 20% reduction in tumor size to say that a cancer therapy was actively working. This has changed, however, with the introduction of newer targeted therapies.

Targeted therapies are drugs that specifically target mechanisms of growth in cancer to stop the growth and prevent further spread. They do not, however, usually "cure" cancer.

With the introduction of targeted therapies, treatment response is now described with terms such as progression-free survival and an overall survival benefit. If the treatment keeps cancer in check—allowing people longer survival with minimal symptoms—then stable disease could very well apply irrespective of the tumor size.

Impact of Immunotherapy

Stable disease can also be considered a positive sign in people provided newer immunotherapy drugs. Traditionally, doctors have aimed to achieve the fastest response when dealing with cancer. Chemotherapy drugs, for example, are used in first-line treatment because they kill cancer cells almost immediately.

Immunotherapy drugs work in a different way. They "take the brakes off" the immune system so that your own immune cells can fight cancer.

There is another phenomenon seen with immunotherapy that can also affect response, or at least the appearance of a response, on imaging studies. Referred to as pseudoprogression, it is an uncommon condition in which a tumor appears to have grown in response to immunotherapy even if it hasn't.

It is now thought that the immunologic response can affect cells surrounding a tumor, creating benign lesions that mimic cancer cells on a CT or PET scan. In some cases, a biopsy may reveal that the tumor has completely disappeared and that all that is left are the residual lesion.

Pseudoprogression most often occurs with lymph nodes but may also affect the kidneys, liver, lungs, adrenal gland, and chest and abdominal walls.

Other Terms Describing Cancer Response

There are different terms your oncologist may use in describing your response to cancer treatment. While many of the terms are considered standard, the criteria for diagnosis are ever-evolving, and there are often challenges in standardizing definitions between health authorities and researchers.

Today, there are several different criteria used by oncologists, including those established by the World Health Organization (WHO) and others known as the Response Evaluation Criteria in Solid Tumors (RECIST), the Immune-related Response Criteria (IRC), and the Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST).

Regardless of the criteria used, diagnoses are based on the changes in the size of target and non-target tumors.

Some of the more commonly used terms include the following:

• Complete response (CR) is used when there is no evidence of cancer after treatment. Also referred to as complete remission or no evidence of disease (NED), it does not always mean the cancer is cured.
• Duration of response (DoR) is the length of time that a tumor continues to respond to treatment without the cancer growing or spreading.
• Overall response rate (ORR) is the proportion of patients in a trial whose tumor is destroyed or significantly reduced by a drug (useful in deciding which drug is best for you).
• Partial response (PR), also known as partial remission, is defined as a decrease of more than 30% in the size of the longest diameter of a target tumor from the baseline.
• Progressive disease (PD) is defined as an increase of more than 20% in the size of the longest diameter of a target tumor from the baseline.
• Progression-free survival (PFS) is how long a person lives without the cancer worsening (useful in establishing the prognosis for a patient).
• Recurrence is the return of cancer after a period of complete remission when no cancer was detected. The recurrence can be local (occurring in the same area as before), regional (found in nearby lymph nodes), or distant (found in an entirely different part of the body).
• Unequivocal progression (UP) is diagnosed when there is a substantial worsening of the disease. Even if the target tumors are stable, UP would be declared if the number or size of non-target tumors have increased substantially enough to suggest that the current therapy is no longer working.

A Word From Verywell

Given that metastatic cancer is responsible for up to 90% of all cancer deaths, the fear of progression or recurrence can be overwhelming for some. Even if your cancer is advanced, being told that you have stable disease should be reassuring. It means that your current treatment is able to impede the spread of cancer and may do so for the foreseeable future.